package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;
import java.util.Optional;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if(objects.size()==1){
            return (T) objects.get(0);
        }else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int update(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();

        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);

        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public int insert(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();

        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);

        return simpleExecutor.insert(configuration, mappedStatement, params);
    }

    @Override
    public int delete(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();

        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);

        return simpleExecutor.delete(configuration, mappedStatement, params);
    }



    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, (proxy, method, args) -> {
            // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
            // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
            // 方法名：findAll
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();

            String statementId = className+"."+methodName;
            MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
            Object result;
            //判断mapper中的方法类型，最终调用的还是SqlSession中的方法
            switch (mappedStatement.getSqlCommandType()) {
                case INSERT: {
                    return insert(statementId, args);
                }
                case UPDATE: {
                    return update(statementId, args);
                }
                case DELETE: {
                    return delete(statementId, args);
                }
                case SELECT:
                    // 准备参数2：params:args
                    // 获取被调用方法的返回值类型
                    Type genericReturnType = method.getGenericReturnType();
                    // 判断是否进行了 泛型类型参数化
                    if (genericReturnType instanceof ParameterizedType) {
                        List<Object> objects = selectList(statementId, args);
                        return objects;
                    }

                    return selectOne(statementId, args);
                default:
                    throw new RuntimeException("Unknown execution method for: " + mappedStatement.getSqlCommandType());
            }
        });

        return (T) proxyInstance;
    }


}
